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排序方式: 共有91条查询结果,搜索用时 31 毫秒
71.
Eimutis Juzeliūnas Konstantinas Leinartas Meilutė Samulevičienė Aloyzas Sudavičius Povilas Miečinskas Remigijus Juškėnas Vaclovas Lisauskas 《Journal of Solid State Electrochemistry》2002,6(5):302-310
A quartz crystal microbalance (QCM) has been used for in situ corrosion studies of magnetron-sputtered Co-Cr-Mo and Ni-Cr-Mo
alloys, which are of great importance in various technical and medical applications. The corrosion monitoring has been performed
in an oxygen-containing atmosphere and in NaCl solution. The alloys were deposited on quartz substrates by means of DC magnetron
sputtering. X-ray photoelectron spectroscopy analysis showed that the composition of the deposits was similar to that of the
magnetron-sputtering targets. X-ray diffraction revealed an amorphous structure of the sputtered deposits, while the casting
alloys had a crystalline structure. The polarization resistance of sputtered alloys in NaCl solution was higher than the activity
of conventional alloys, which implied a superior corrosion resistance of the sputtered deposits. Corrosion was initiated by
supplying oxygen gas into a wet argon atmosphere and the QCM detected corrosion with nanogram resolution as the increase in
mass. Corrosion currents were calculated from the mass versus time curves. The QCM appeared to be an effective tool for corrosive
characterization of sputtered alloys in gaseous environments. A corrosion current calculation in solution was complicated
by metal transfer to the liquid phase.
Electronic Publication 相似文献
72.
Kamoto M Umezawa N Kato N Higuchi T 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(26):8004-8012
The introduction of hexahistidine (His tag) is widely used as a tool for affinity purification of recombinant proteins, since the His tag binds selectively to nickel-nitrilotriacetic acid (Ni(2+)-NTA) complex. To develop efficient "turn-on" fluorescent probes for His-tagged proteins, we adopted a fluorophore displacement strategy, that is, we designed probes in which a hydroxycoumarin fluorophore is joined via a linker to a metal-NTA moiety, with which it forms a weak intramolecular complex, thereby quenching the fluorescence. In the presence of a His tag, with which the metal-NTA moiety binds strongly, the fluorophore is displaced, which results in a dramatic enhancement of fluorescence. We synthesized a series of hydroxycoumarins that were modified by various linkers with NTA (NTAC ligands), and investigated the chemical and photophysical properties of the free ligands and their metal complexes. From the viewpoint of fluorescence quenching, Ni(2+) and Co(2+) were the best metals. Fluorescence spectroscopy revealed a 1:1 binding stoichiometry for the Ni(2+) and Co(2+) complexes of NTACs in pH 7.4 aqueous buffer. As anticipated, these complexes showed weak intrinsic fluorescence, but addition of a His-tagged peptide (H-(His)(6)-Tyr-NH(2); Tyr was included to allow convenient concentration measurement) in pH 7.4 aqueous buffer resulted in up to a 22-fold increase in the fluorescence quantum yield. We found that the Co(2+) complexes showed superior properties. No fluorescence enhancement was seen in the presence of angiotensin I, which contains two nonadjacent histidine residues; this suggests that the probes are selective for the polyhistidine peptide. 相似文献
73.
Felix Trottmann Keishi Ishida Jakob Franke Aleksa Stanii Mie Ishida‐Ito Hajo Kries Georg Pohnert Christian Hertweck 《Angewandte Chemie (International ed. in English)》2020,59(32):13511-13515
Pathogenic bacteria of the Burkholderia pseudomallei group cause severe infectious diseases such as glanders and melioidosis. Malleicyprols were identified as important bacterial virulence factors, yet the biosynthetic origin of their cyclopropanol warhead has remained enigmatic. By a combination of mutational analysis and metabolomics we found that sulfonium acids, dimethylsulfoniumpropionate (DMSP) and gonyol, known as osmolytes and as crucial components in the global organosulfur cycle, are key intermediates en route to the cyclopropanol unit. Functional genetics and in vitro analyses uncover a specialized pathway to DMSP involving a rare prokaryotic SET‐domain methyltransferase for a cryptic methylation, and show that DMSP is loaded onto the NRPS‐PKS hybrid assembly line by an adenylation domain dedicated to zwitterionic starter units. Then, the megasynthase transforms DMSP into gonyol, as demonstrated by heterologous pathway reconstitution in E. coli. 相似文献
74.
Dr. Dymytrii Listunov Prof. Ole Hammerich Irving Caballero-Quintana Dr. Albert Poater Cécile Barthes Dr. Carine Duhayon Dr. Mie Højer Larsen Dr. José-Luis Maldonado Dr. Gabriel Ramos-Ortiz Prof. Mogens Brøndsted Nielsen Dr. Valérie Maraval Prof. Remi Chauvin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(47):10707-10711
carbo-Benzene is an aromatic molecule devised by inserting C2 units within each C−C bond of the benzene molecule. By integrating the corresponding carbo-quinoid core as bridging unit in a π-extended tetrathiafulvalene (exTTF), it is shown that a carbo-benzene ring can be reversibly formed by electrochemical reduction or oxidation. The so-called carbo-exTTF molecule was thus experimentally prepared and studied by UV–visible absorption spectroscopy and cyclic voltammetry, as well as by X-ray crystallography and by scanning tunneling microscopy (STM) on a surface of highly oriented pyrolytic graphite (HOPG). The molecule and its oxidized and reduced forms were subjected to a computational study at the density functional theory (DFT) level, supporting carbo-aromaticity as a driving force for the formation of the dication, radical cation, and radical anion. By allowing co-planarity of the dithiolylidene rings and carbo-quinoidal core, carbo-exTTFs present a promising new class of redox-active systems. 相似文献
75.
76.
Electrochemical Behaviour of HOPG and CVD‐Grown Graphene Electrodes Modified with Thick Anthraquinone Films by Diazonium Reduction
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Elo Kibena Margus Marandi Väino Sammelselg Kaido Tammeveski Bjarke B. E. Jensen Anders B. Mortensen Mie Lillethorup Mikkel Kongsfelt Steen U. Pedersen Kim Daasbjerg 《Electroanalysis》2014,26(12):2619-2630
Highly oriented pyrolytic graphite (HOPG) and graphene grown on Ni (Ni‐Gra) or Cu (Cu‐Gra) by chemical vapour deposition were modified with thick anthraquinone (AQ) films (7?60 nm) by redox grafting of the pertinent diazonium salt. Glassy carbon (GC) electrodes were used for comparison. The AQ‐modified GC electrodes showed excellent blocking properties towards the Fe(CN)63?/4? redox probe, although it was noted that in the case of Ni‐Gra and Cu‐Gra, the blocking ability depended strongly on the underlying substrate. Oxygen reduction studies revealed good electrocatalytic activity of AQ‐modified HOPG, Ni‐Gra, and Cu‐Gra, compared with the bare electrodes. 相似文献
77.
Mie KodaniAyumi Takamori Kazuo TakimiyaYoshio Aso Tetsuo Otsubo 《Journal of solid state chemistry》2002,168(2):582-589
Seven conductive radical cation salts based on MDSe-TSF (methylenediselenotetraselenafulvalene) have been synthesized by electrocrystallization in the presence of Cl−, Br−, I3−, I2Br−, PF6−, ClO4−, and Cu(NCS)2− counter anions. The crystal appearances of these salts fairly depend on the anions employed. X-ray crystallographic analyses have revealed that the PF6 and ClO4 salts in the shape of brown thin plates adopt the θ-type structures characterized by the herringbone arrangement of donor stacks, whereas the Cl and Br salts in the shape of black thick plates favor the κ-type structures with the orthogonal arrangement of donor dimers. Regardless of different crystal appearances or crystal packing patterns, all these salts show high conductivity (>102 S cm−1) at room temperature and retain metallic properties down to 4.2 K. Of them, the Br salt shows a weak but distinct diamagnetic shielding signal below 4 K in the dc magnetization measurement under zero-field-cooled (ZFC) condition, suggesting a sign of superconductivity. The band calculations of both PF6 and Br salts demonstrate closed Fermi surfaces indicative of two-dimensional molecular conductors. 相似文献
78.
Dr. Mie Andersen Dr. Andrew J. Medford Prof. Jens K. Nørskov Prof. Dr. Karsten Reuter 《Angewandte Chemie (International ed. in English)》2016,55(17):5210-5214
Bifunctional coupling of two different catalytic site types has often been invoked to explain experimentally observed enhanced catalytic activities. We scrutinize such claims with generic scaling‐relation‐based microkinetic models that allow exploration of the theoretical limits for such a bifunctional gain for several model reactions. For sites at transition‐metal surfaces, the universality of the scaling relations between adsorption energies largely prevents any improvements through bifunctionality. Only the consideration of systems that involve the combination of different materials, such as metal particles on oxide supports, offers hope for significant bifunctional gains. 相似文献
79.
Proton beam is useful to target tumor tissue sparing normal cells by allowing precise dose only into tumor cells. However, the cellular and molecular mechanisms by which proton beam induces tumor cell death are still undefined. We irradiated three different tumor cells (LLC, HepG2, and Molt-4) with low energy proton beam (35 MeV) with spread out Bragg peak (SOBP) in vitro, and investigated cell death by MTT or CCK-8 assay at 24 h after irradiation. LLC and HepG2 cells were sensitive to proton beam at over 10 Gy to induce apoptosis whereas Molt-4 showed rather low sensitivity. Relative biological effectiveness (RBE) values for the death rate relative to gamma-ray were ranged from 1.1 to 2.3 in LLC and HepG2 but from 0.3 to 0.7 in Molt-4 at 11 d after irradiation by colony formation assay. The typical apoptotic nuclear DNA morphological pattern was observed by staining with 4'-6-diamidino-2-phenylindole (DAPI). Tiny fragmented DNA was observed in HepG2 but not in Molt-4 by the treatment of proton in apoptotic DNA fragment assay. By FACS analysis after stained with FITC-Annexin-V, early as well as median apoptotic fractions were clearly increased by proton treatment. Proton beam-irradiated tumor cells induced a cleavage of poly (ADP-ribose) polymerase-1 (PARP-1) and procaspases-3 and -9. Activity of caspases was highly enhanced after proton beam irradiation. Reactive oxygen species (ROS) were significantly increased and N-acetyl cysteine pretreatment restored the apoptotic cell death induced by proton beam. Furthermore, p38 and JNK but not ERK were activated by proton and dominant negative mutants of p38 and JNK revived proton-induced apoptosis, suggesting that p38 and JNK pathway may be activated through ROS to activate apoptosis. In conclusion, our data clearly showed that single treatment of low energy proton beam with SOBP increased ROS and induced cell death of solid tumor cells (LLC and HepG2) in an apoptotic cell death program by the induction of caspases activities. 相似文献
80.
Povilas?Mie?inskas Konstantinas?Leinartas Virginija?Uksien? Eimutis?JuzeliūnasEmail author 《Journal of Solid State Electrochemistry》2007,11(7):909-913
The study demonstrated a possibility to sense the activity of microorganisms on metals in situ under atmosphere conditions
using a quartz crystal microbalance (QCM) as a sensitive mass change detector. Other innovative aspects of the QCM application
include long-term monitoring (over month), taking count of the influence of atmospheric pressure and application of Al-glued
foil electrodes. The research subject was aluminium colonisation by Aspergillus niger Tiegh., a filamentous ascomycete fungus. The difference between the QCM data for abiotic and biotic samples reflected microbiological
activity, which resulted in exponential mass gain during exposure. The increase in mass was due to various phenomena, i.e.
development of biomass, secretion of metabolites, water uptake by the colony and microbially induced corrosion. The glued
foil method demonstrated a possibility to expand the scope of the QCM studies from evaporated, sputtered or electroplated
materials to those, from which thin foils may be produced.
Dedicated to Professor Dr. Algirdas Vaškelis on the occasion of his 70th birthday. 相似文献